Role of Ataxin-1 in BACE1 Expression and Alzheimer's Disease

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Project Summary Recent efforts to uncover genetic factors responsible for Alzheimer's disease (AD) have identified dozens of associated loci. Among these, our research group previously reported ATXN1 in a family-based AD genome-wide association study. ATXN1 has been otherwise known for to harbor mutations causing spinocerebellar ataxia type 1, a neurodegenerative disease that primarily impairs coordinated movement. In a cell-based study, knockdown of Ataxin-1 gene (ATXN1) expression increased amyloidogenic processing of the amyloid precursor protein (APP) and the secretion of A, the main component of senile plaques in AD brains. In the preliminary examination of Ataxin-1 KO mice, we found Ataxin-1 regulates BACE1 expression, selectively in AD-vulnerable brain regions. In AD mice, depletion of Ataxin-1 increased -secretase-cleavage of APP, A deposition and gliosis in the cerebrum. Furthermore, Ataxin-1 KO impaired hippocampal neurogenesis and axonal targeting, which are regulated by BACE1. To validate and expand upon these findings, here, we propose to 1. Elucidate the molecular mechanism by which Ataxin-1 regulates BACE1 expression in the brain; 2. Assess the impact of Ataxin-1 loss of function on AD pathogenesis; and 3. Identify and characterize novel AD-associated Ataxin-1 gene variants and/or mutations from AD DNA sample sets. Specifically, for Aim 1, we will first determine whether Ataxin-1 regulates BACE1 mRNA level by affecting its stability or by its transcription. To test this, we will employ acute brain slice cultures of Ataxin-1 KO and WT mice, and examine the differential effects of transcriptional inhibitors on the steady-state level of BACE1 mRNA and also measure newly synthesized BACE1 mRNA incorporating nucleotide analogs in the cultured slices. We will then examine if Ataxin-1-interacting transcriptional factors bind to and regulate BACE1 promoter by ChIP analysis. With regard to Aim 2, we will examine if the increased A plaque load and gliosis are maintained in APP-PS1/ATXN1-KO mice at older age (9 month). To determine if impaired hippocampal neurogenesis and axonal targeting are caused by increased BACE1, we will generate ATXN1 −/−:BACE1 +/− mice and examine if the two deficits are rescued, as compared to ATXN1 −/− mice. Finally, in Aim 3, we will identify ATXN1 mutations/variants that either increase risk or confer protection for AD by analysis of WGS/WES data of NIMH, NIA and ADNI AD DNA sample sets. For the most associated mutations/variants, we will examine their effects on BACE1 expression and APP processing by incorporating them into the genome of human neuronal cells via CRISPR/Cas9 technology. At the completion of the proposed study, we believe we will provide critically needed data addressing the role of Ataxin-1 in regulating BACE1 expression while also facilitating novel therapies aimed at targeting BACE1 to prevent and treat AD.